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NASA Compares Hurricanes Isaac and Katrina: 7 Years Apart
08.31.12
 
TRMM's Precipitation Radar were used to construct these 3D images of Isaac and Katrina. › View larger image
TRMM's Precipitation Radar were used to construct these 3D images of Isaac and Katrina. Katrina (on the right) appears as a very symmetrical storm, a sign of a strong circulation, with a well-defined eye (in the center of the cut-away view) surrounded by a complete eyewall containing an area of deep convective towers (shown in red). Isaac (on the left), on the other hand, though surrounded by rainbands that spiral in towards the center is less symmetrical and does not have a distinctive eye though it too has some deep convective towers near its center (shown in red).
Image Credit: SSAI/NASA, Hal Pierce
NASA Compares Hurricanes Isaac and Katrina: 7 Years Apart

With Hurricane Isaac making landfall on the northern Gulf coast almost 7 years to the day that Hurricane Katrina made landfall and in almost the same location in southeastern Louisiana that Katrina did, it is natural to compare the two storms.

Katrina of course will always be remembered for the massive storm surge that inundated large portions of the northern Gulf coast, reaching almost 28 feet (8.5 meters) along the Mississippi coast, breaking the previous mark of 24 feet (7.3 meters) left there from Hurricane Camille. Like Katrina, Isaac was also a large storm with both measuring roughly 248 miles (400 km) in size. Big storms have bigger wind fields, which allow them to push against the ocean surface over a large area, increasing the potential for storm surge for a given area of coastline.

Fortunately, Isaac impacted the coast as a much weaker Category 1 hurricane and was a tropical storm prior to that; Katrina made landfall as a much more powerful Category 3 storm and was previously an extremely powerful Category 5 storm. At one point, Katrina had hurricane force winds extending up to 75 miles (120.7 km) from the center. So far preliminary reports indicate that Isaac's storm surge may have reached up to 12 feet in parts of Louisiana, which is quite substantial for a "mere" Category 1 storm. Of course the surge can vary according to the shape of the coastline and seafloor, but 12 feet (3.6 meters) is more in line with a Category 3 storm than a 1 and shows how size can be an important factor.

TRMM's Precipitation Radar (PR) can provide a unique perspective on hurricanes. Data from the PR were used to construct these 3D images of Isaac and Katrina. Katrina (on the right) appears as a very symmetrical storm, a sign of a strong circulation, with a well-defined eye (in the center of the cut-away view) surrounded by a complete eyewall containing an area of deep convective towers (shown in red). Isaac (on the left), on the other hand, though surrounded by rainbands that spiral in towards the center is less symmetrical and does not have a distinctive eye though it too has some deep convective towers near its center (shown in red).

Actually, for most of its life, Isaac lacked a core and only really began to organize and intensify when it neared the coast, which was when the data for this image was collected. Isaac's lack of a core greatly inhibited its intensification and was most likely due to dry air intrusions. This is somewhat evidenced by the gaps in the surrounding precipitation field (visible as the blue and black valleys). Were it not for the dry air entering its circulation, Isaac may have arrived at the Gulf coast looking but much more like Katrina. At the times that the data for these two images were collected by the TRMM PR, Katrina was a rapidly-deepening Category 3 hurricane in the central Gulf of Mexico on its way to Category 5 with sustained winds already at ~115 mph (100 knots) and quickly increasing, and Isaac was a recently-upgraded Category 1 hurricane near the coast of Louisiana with sustained winds of ~80 mph (70 knots).

TRMM is a joint mission between NASA and the Japanese space agency JAXA.

 
 
Text Credit: Steve Lang
SSAI/NASA Goddard Space Flight Center, Greenbelt, Md.